1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and testing method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for increasing yield by preventing an unnecessary waste of parts.
2. Description of the Related Art
As the information society develops, the importance of a display device as a visual information transmission medium increases. A cathode ray tube (CRT) or Braun tube is currently the typical display device. However, the CRT has problems in that its weight and size are too large. Unlike the CRT, various types of flat panel display devices have been developed are light-weight and have a thin profile. These types of flat panel display devices include liquid crystal display (LCD), field emission display FED, plasma display panel PDP, electro-luminescence EL, and other types of flat panel devices that are practical to use and on the market.
The liquid crystal display device can satisfy the current trend in electronic devices of being thin, light-weight, and small. As the efficiency in the productivity in LCD devices improves, LCD devices will rapidly supersedes the cathode ray tube in a many applications.
In general, there are two types of LCDs. The first type is an active matrix LCD and the second type is a passive matrix type. In a passive matrix type LCD, each of the cells are switched externally. In the active matrix type LCD, each of the cell are switched internally by a thin film transistor (TFT). The active matrix type LCD has advantages in that picture quality is excellent and power consumption is low. Further, the active matrix type LCD can be manufactured so as to have a large size and to have high resolution due to a recent advances in mass production technology, which resulted from research and development. A process for fabricating the active matrix type LCD can be divided into substrate cleaning, substrate patterning, alignment film forming/rubbing, substrate bonding/liquid crystal injecting, mounting, inspecting and repairing. In the substrate cleaning process, impurities contaminated in a substrate surface are removed with a cleaning solution.
The substrate patterning process is divided into an upper substrate (or color filter substrate) patterning and lower substrate (or TFT-array substrate) patterning. A color filter, a common electrode and a black matrix are formed on an upper substrate in the upper substrate patterning. A signal wire lines, such as data lines and gate lines, are formed on a lower substrate, and a cell thin film transistor (hereinafter, referred to as “cell TFT”) is formed adjacent to a crossing of the data line and the gate line in the lower substrate patterning. And, a pixel electrode is formed at a pixel area between the gate line and the data line connected to a source electrode of the cell TFT.
In the alignment film forming/rubbing process, an alignment film is formed on at least one of the upper substrate and the lower substrate. Then, the alignment film is rubbed with a rubbing cloth. If alignment films are formed on both of the substrates, the alignment films are rubbed in the same direction.
In the substrate bonding/liquid crystal injecting process, the upper substrate and the lower substrate are bonded with a sealant. Then, a liquid crystal and a spacer are injected through a liquid crystal injection hole in the sealant. Subsequently, a sealing process is performed on the liquid crystal injection hole.
In the mounting process of the liquid crystal display panel, a tape carrier package (hereinafter, referred to as “TCP”) on which an integrated circuit, such as a gate drive integrated circuit and a data drive integrated circuit are mounted, is connected to a pad part of the lower substrate. The drive integrated circuit can also be directly mounted on the lower substrate by a chip-on-glass (hereinafter, referred to as “COG”) method other than a tape automated bonding method.
The inspecting process includes an electrical inspection performed after forming the various signal lines and the pixel electrode on the lower substrate; an electrical inspection performed after the substrate bonding/liquid crystal injecting process; and macrography inspection.
The repairing process performs restoration of a substrate or panel, which is judged to be repairable during the inspecting process. On the other hand, defective substrates which are judged to be unrepairable in the inspecting process are disposed as a waste.
The electrical inspection after the substrate bonding/liquid crystal injecting process is mainly composed of a picture quality inspection that includes a cross-talk inspection and a brightness inspection of each gray level. The electrical inspection is performed when a data drive circuit and a gate drive circuit are connected to the signal line of the TFT array substrate, as shown in FIGS. 1 and 2.
As shown in FIG. 1, an inspecting method of the related art connects a data switching TFT (hereinafter, referred to as “Tdata”) to lower ends of the data lines DL. Further, the related art inspecting method attaches a gate switching TFT (hereinafter, referred to as “Tgate”) for supplying an inspection gate pulse to the gate lines at the same time in the gate lines GL. Furthermore, another switching TFT (hereinafter, referred to as “Tmuxe”) is connected to the top ends of the data lines DL of a pixel matrix array in which the liquid crystal cells Clc and the cell TFT's are formed, to act to supply a data voltage, which is supplied from output terminals of the data drive circuit 10 of the TCP or COG. A set of external contact pads 11 includes a MUX1 pad, a MUX2 pad and a MUX3 pad for controlling the Tmuxes; a VEGATE pad for supplying a voltage to a gate terminal of the Tgate; a VGATE pad for supplying a gate high voltage and a gate low voltage to a source terminal of the Tgate; a VEDATA pad for supplying a voltage to a gate terminal of the Tdata; and a VDATA pad for supplying a test data voltage to source terminals of the Tdatas.
If the set of the external contact pads 11 is connected to output terminals of a test jig, a test data voltage can be supplied to the data lines DL through the VDATA pad via Tdata, and a gate high voltage is supplied to the gate lines GL through the VGATE pad via the Tgate. As a result, the TFT's of the pixel array are turned on so as to apply the test data voltage to the liquid crystal cells, thereby enabling inspection of whether there is a gray level expression defect in any of the liquid crystal cells.
During this inspecting method, the gate drive circuits 13 in a TCP can be attached to the liquid crystal display panel, as shown in FIG. 2, to sequentially supply a gate pulse to the gate lines GL, thereby sequentially selecting the liquid crystal cells of a horizontal line to which the test data voltage is to be supplied. Further, for inspecting the cross-talk, the inspecting method of the related art displays a mid gray level on the outer perimeter with black on the inside followed by white in the pixel matrix array of the liquid crystal display panel, as shown in FIG. 3. Thus, at least two different test data are supplied to the data lines DL, but the same data cannot be supplied to the data lines by the VDATA via Tdata formed in the liquid crystal display panel of FIGS. 1 and 2. Accordingly, a data drive circuit 10 is connected to the Tmux of the liquid crystal display panel in a COG or TCP form. In other words, according to the related art inspecting method, when performing the cross-talk inspection, the data drive circuit must be attached to the liquid crystal display panel in the TCP or COG form to determine whether or not there is a cross-talk defect. However, it is inevitable that the TCP or COG attached to the liquid crystal display panel, which is judged to be defective by a cross-talk inspection, will have to be discarded because it is attached to a defective liquid crystal display panel. Thus, data drive circuits will be wasted and thus decrease overall yield of data drive circuits.